1. Field of the Invention
The field of invention relates to the production of aromatics from naphtha. More specifically, the field relates to a system and method for maximizing aromatic product production while satisfying gasoline production demand using straight run and hydrocracked naphtha.
2. Description of the Related Art
Two major sources of naphtha for both direct gasoline blending and the production of gasoline blending components are straight run naphtha and hydrocracked naphtha. Straight run naphtha is the atmospheric distillation oil cut from the crude distillation column. Hydrocracked naphtha is one of several products from a hydrocracking unit. A hydrocracking unit takes feeds, including cat cracker “cycle oil”, visbreaker gas oils and coker unit gas oils, and breaks down the long-chain paraffins and aromatics, especially the heavy aromatic, polynuclear aromatic and heteroaromatic fractions in the oils, into smaller paraffins and aromatics. The hydrocracker produces several streams, including a naphtha stream that contains lower molecular weight normal and cyclo-paraffins, olefins and aromatics with shorter alkyl chain moieties.
Crude oil refiners extract aromatics, especially BTEXs (benzene, toluene, ethyl benzene and the xylenes), as petrochemical feedstocks. Environmental regulations on fuels are promoting the reduction or outright elimination of C6-8 aromatics in gasoline.
Traditional gasoline blending component production systems separate hydrocracked naphtha into light and heavy naphtha fractions for use not only in forming gasoline-blending components but also for direct blending into gasoline fuels. Light hydrocracked naphtha includes paraffins and olefins with lesser amounts of naphthenes and aromatics. Iso-paraffins and aromatics suitable for gasoline blending form after separation, isomerization or reformation of the light hydrocracked naphtha. Heavy hydrocracked naphtha includes aromatics with a portion of heavier paraffins and mono- and di-olefins. Refiners direct a portion of the heavy hydrocracked naphtha to the gasoline blending “pool”, which are storage tanks that the gasoline blending facility uses to mix gasoline blending components to make regular and premium grades of motor fuel. Heavy hydrocracked naphtha boosts the research octane number (RON) of the blended fuel because of its aromatic content. Refiners direct the remainder of the heavy hydrocracked naphtha to reforming and aromatics separations units to create valuable refined aromatic products.
Traditional gasoline blending component production systems do not maximize the potential for capturing aromatics from the heavy portions of the hydrocracked naphtha. Aromatics are valuable commodity chemicals for specialized chemical and polymer production. Gasoline blending operations do require a volume of hydrocracked naphtha for creating suitable amounts of products at an appropriate RON value.